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I have a couple variables a , b and c.

On a for loop I wanted to display all their values.

for i in ${!a[@]}; do
  echo "${a[$i]} ${b[$i]} ${c[$i]}"
done

Now values are shifted to the top since other values in variable c are intentionally empty.

mammals land elephant
reptile water pigeon
birds air

How do I create an empty variable so that the values won't get shifted?

I tried doing if the string matches "water" then it will echo only a and b.

for i in ${!a[@]}; do
  if [ "$c" = "water"]; then
  echo "${a[$i]} ${b[$i]}"
  else
  echo "${a[$i]} ${b[$i]} ${c[$i]}"
  fi
done
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6
  • Values are not shifted when outputting the values. The problem lies in the way how you populate the arrays. Commented Mar 29, 2020 at 10:33
  • How do you populate the arrays? Commented Apr 15, 2020 at 8:00
  • Previous edit shows how I have populated them @Kusalananda Commented Apr 15, 2020 at 8:16
  • So I rolled back the edit where you deleted that bit. Commented Apr 15, 2020 at 9:22
  • In the last bit of code, you seem to be using EMPTY as an array, even though it's not. You also use the array c as a non-array in the test. Are these typos in the question only? Commented Apr 15, 2020 at 9:23

1 Answer 1

Reset to default
4

Are you looking for something like this?

a=("" b c)
b=(d "" f)
c=(g h "")

for i in ${!a[@]}; do
  printf "%s\t" "${a[$i]}" "${b[$i]}" "${c[$i]}"
  echo          
done

The output is

$ bash arr.sh 
        d       g
b               h
c       f

I used empty strings to mark "missing" values on the diagonal. In the compound assignment, it's not possible to skip an index, there has to be something there. Of course you could use a[1]=b a[2]=c and leave a[0] unassigned instead, or explicitly unset a[0].

I you need a proper two-dimensional array, you might want to use a proper programming language and not the shell... Some sort of a workaround might be to use associative arrays with keys like 2-3, with the two indexes delimited by some string. But it depends on what you're actually doing.

(In your latter snippet, you're using $c without an index (getting the same as ${c[0]}, and then using an index on EMPTY, even though you only assigned one value to it.)

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3
  • I tried your solution and doesn't work for me since $c returns only the result from the example is "elephant" and "pigeon". Commented Mar 29, 2020 at 12:10
  • Trying to use the latter suggestion you made. Almost solved it but it doesn't return back to the else statement after printing the empty values. Commented Mar 29, 2020 at 13:09
  • 1
    @sudo it is very difficult to help you if you can't give us a reproducible example. Please edit your question and show us how you are populating your arrays and also show us what output you want to see. At the moment, we need to guess. Commented Mar 31, 2020 at 10:00

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